Wheel slip detection device

ABSTRACT

To detect transition from rolling to sliding of a wheel over a surface, a transducer coupled to the wheel provides output pulses having a repetition rate representative of wheel speed. The pulses are applied to a logic circuit including a pair of multivibrators, one of which has a variable time circuit setting its unstable state in dependence on pulse repetition rate; the rate itself is sensed by applying the pulses from the two multivibrators to a coincidence gate which activates a wheel slip detector (and, if desired, an override control to a brake, or accelerating arrangement for the wheel).

United States Patent Gunsser et a1.

[ 51 Apr. 25, 1972 [54] WHEEL SLIP DETECTION DEVICE [72] Inventors: Peter Gunsser, Stuttgard; Klaus H. Christ,

Stuttgart-Durrlewang, both of Germany [30] Foreign Application Priority Data Nov, 27, 1968 Germany ..P 18 11 192.7

3,130,805 4/1964 Carter et al. ..340/53 X 3,233,946 2/1966 Lockhart ...340/262 X 3,245,213 4/1966 Thompson et a1. ..340/262 X Primary E.\-aminerAlvin H. Waring Att0rneyFlynn & Frishauf [5 7] ABSTRACT To detect transition from rolling to sliding of a wheel over a surface, a transducer coupled to the wheel provides output pulses having a repetition rate representative of wheel speed. The pulses are applied to a logic circuit including a pair of multivibrators, one of which has a variable time circuit setting its unstable state in dependence on pulse repetition rate; the rate itself is sensed by applying the pulses from the two multivibrators to a coincidence gate which activates a wheel slip detector (and, if desired, an override control to a brake. or accelerating arrangement for the wheel).

11 Claims, 9 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,927,302 3/1960 Steigerwald ..340/262X PATENTEMPR 25 1912 SHEET 30F 4 from baffery WHEEL SLIP DETECTION DEVICE The present invention relates to a system to detect transition of rolling to slipping of wheels over a surface, for example when the wheel is rapidly accelerated or sharply braked, and more particularly to such a system intended for association with braking, or acceleration control systems to prevent slipping of the wheel and thus skidding, or loss of tractive effort, essentially without delay.

Upon braking of moving vehicles, it is important that the wheels do not block since they then will slide over the way surface which, in case of untracked vehicles will cause skidding. The coefficient of friction between a sliding, or slipping wheel and the surface is substantially less than the coefficient of friction between the wheel and the surface when it is still rolling. Slipping of wheels must be avoided not only to prevent skidding, but also to maintain high braking effort. Wheels are blocked when the force from wheel to surface in the longitudinal direction of the vehicle is greater than the component of the adhesive force due to the frictional coefficient between wheel and surface, which is perpendicular to the wheel axle. This component depends on the loading of the wheel and is proportional thereto; the braking effort is initially controlled by pressure of the brake shoes against the brake drums, or brake discs, as well known.

Braking of a vehicle on a straight track causes a shift in loading weight on the wheels. The rear wheels are less loaded, the front wheels increasingly loaded, causing the well known brake dip." In order to avoid blocking of the rear wheels as the effective weight of the vehicle shifts, the braking effort on the rear wheels must be decreased with respect to the braking effort acting on the front wheels. To increase reliability of braking in a curve, the braking effort on the separate wheels must further be differently distributed between transversely aligned wheels, so that the wheels at the outside of the curves are braked more effectively than those at the inner side of the curve.

The problems arising in braking of vehicles are similar to those which arise upon acceleration. Slipping, or spinning of drive wheels, upon acceleration, may cause skidding. Tracked vehicles may suffer substantial loss in running time upon spinning of drive wheels during acceleration.

Various braking control systems to sense and control braking efforts in vehicles have previously been proposed, usually inhibiting braking effort from being transmitted to the wheels if the wheels are excessively decelerated. Such deceleration of a wheel, in excess of a predetermined level, may indicate the 'begin of a skid. Electric pulse sources are known in which, by

relative movement between an inertia body and the drive shaft of the wheel, excessive acceleration, or deceleration causes a contact element to operate furnishing an electrical pulse. The pulse source, being mechanically operated, is subject to the usual difficulties arising in connection therewith, that is wear and tear, time delay, and possible malfunction due to dirt and the like. Additionally, the inherent time delay in the devices as heretofore used may be of such order that it cannot be ignored, so that sliding may occur before corrective measures in the brake, or drive system can be initiated.

It is an object of the present invention to provide a slip detection system which is not subject to wear and tear and operates essentially without any time delay.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the wheel (or its shaft) is provided with a pulse source such as a rotating magnet without mechanical contact with a fixed element such as a coil, to provide pulses which are then analyzed in a logic circuit sensing elapsed time between the pulses. When the elapsed time between pulses deviates from a predetermined value, an output signal is derived which can be used to control a braking, or accelerating system to decrease the power (braking, or accelerating) transfer to the wheel and thus prevent wheel slip.

The logic circuit preferably includes a pair of monostable multivibrators and a coincidence circuit. The pulses derived from the transducer are applied to the first monostable multivibrator, the output of which is connected to the coincidence circuit. Additionally, the output of the first monostable multivibrator is used to trigger the second monostable vibrator which is so constructed, for example by having an integrator circuit connected thereto, that the unstable time of the second multivibrator depends on the time duration between pulses; the output of the second monostable multivibrator is then also applied to the coincidence circuit as a second input. Absence of a predetermined logical relationship between the pulses from the two multivibrators then causes the coincidence gate to furnish a signal, indicative of a duration between input pulses (and, thus pulses from the first monostable multivibrator) deviating from a predetermined level by a preset amount.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic arrangement of the slip detection device for blocking of wheels;

FIG. 2 is a block circuit diagram of a portion of the system of FIG. 1;

FIG. 3 is a schematic diagram of an integrating stage;

FIG. 4 is a schematic representation of a suitable transducer;

FIG. 5 is a series of timing diagrams illustrating voltage relationships in the circuit of FIG. 2;

FIG. 6 illustrates, schematically, an optical scanning arrangement;

FIG. 7 is aschematic arrangement of the slip detection device to detect spinning of a wheel;

FIG. 8 is a block circuit diagram for use in the system of FIG. 7; and

FIG. 9 is a series of timing diagrams illustrating voltage relationships in the circuit of FIG. 8.

A wheel 11 rolls over a way surface 12. Wheel 11 is coupled to a shaft 13 having a brake disc 14 subject to braking effort by a pair of brake shoes 17, 17, activated over links 16, 16 from a brake cylinder 15. The action of brake cylinder 15, itself, is controlled from a brake pedal 23 secured to a fixed part of the vehicle schematically indicated at 24, and acting over a linkage 22.

A pulse source 18 is connected to shaft 13 to rotate therewith. The output of pulse source 18 is connected to a logic circuit 19 which has an output likewise controlling an additional input of brake cylinder arrangement 15.

Depression of brake pedal 23 by the operator causes braking of the vehicle. The brake pedal pressure is transmitted over linkage 22, master cylinder 21, to brake cylinder 15 and then to the wheels. If the braking effort is excessive, wheel 11 will block so that, instead of rolling, it will slip. Pulse generator 18 all the time supplies pulses, the distance between which depends on the circumferential speed of wheel 1 l. The distance between pulses is measured by circuit 19. If the change in distance between pulses supplied from generator 18 exceeds a predetermined value, logic circuit 19 provides a signal which is applied to brake cylinder system 15 in such a direction that the braking effort exerted by brake shoes 17 on brake disc 14 is decreased. The distance of pulses supplied by pulse generator 18 decreases with decreasing speed of the vehicle, and thus decreasing circumferential speed of wheel 11. The distance between pulses which cause logic circuit 19 to supply an output signal to braking cylinder system 15 is made dependent on the speed of wheel 11.

FIG. 2 illustrates the details of logic circuit 19, in block diagram form. The output of pulse source 18 is connected to a monostable multivibrator (flip-flop) 28, having two outputs. One output of stage 28 is connected to one input of a coincidence stage 29. The other output of stage 28 is connected to a second monostable multivibrator (flip-flop) stage 31 and, further, to the input of an integrator 32. The output of the integrator 32 is connected to a second input of monostable multivibrator stage 31, to control the unstable time thereof. The

output of stage 31 is connected as a second input to coincidence stage 29. The output of coincidence stage 29 is connected to an amplifier 33, the output of which is utilized to control the power applied to brake cylinder 15 (or, if the slip under acceleration is to measured, to a prime mover) to control the power transfer.

Integrator 32 is illustrated in detail in FIG. 3. Input terminal 35 is series connected with a resistance 37; the other end of resistance 37 is connected to a junction 36 whichhas a condenser 39 connected to a ground line 38 and one terminal of a further resistance 43 connected thereto. The other terminal of resistance 43 connects with the output terminal 42 and with a condenser 44, which is likewise connected across ground. This is a simple integrating stage which can readily be constructed as a single integrated circuit network; other integrators can be used, for example Miller integrators utilizing semiconductors. The pulse generator'is shown in FIG. 4; a toothed wheel 46, for example of ferromagnetic material, is connected to rotate with the wheel 13, for example by being connected to its shaft. The salient teeth 47 are located beneath a ferromagnetic yoke 48, which is horseshoe-shaped and has a coil 49 having terminals 51, 52 wound therearound. Yoke 48 has a pair of pole pieces which either match teeth 47 of wheel 46, or are opposite the gaps between the teeth. A constant direct current is applied to coil 49. Depending on the position of wheel 46, that is whether the teeth, or the gaps between the teeth are opposite the pole pieces of yoke 48, the reluctance of the path will be high or low. Thus, the inductivity of coil 49 will change periodically and the direct current through coil 49 will have an alternating current component super imposed thereover. The

alternating current component can be taken off by means of a capacitor (not shown). Various other constructions are also possible, for example wheel 46 mayhave a plurality of magnets of different polarity located along its circumference.

These magnets can be secured directly to a non-magnetic wheel. Alternatively, the wheel may be made out of a material which will retain magnetism, and magnetic zones are impressed along the circumference thereof. Again, a yoke is then arranged, with a small air gap, opposite the wheel with the magnets at its circumference, the yoke having pole faces located opposite poles of opposite polarity. A coil located on the yoke will then have positive and negative voltage pulses applied thereto, the number of pulses depending on the speed of the wheel. 1

OPERATION Pulses supplied from coil 49, and taken off capacitatively, are connected to a suitable pulse shaping circuit which may be part of the pulse generator 18, so that they will all be of uniform polarity, for example positive pulses 118 (FIG. 5). The repetition rate, or in other words, the elapsed time between pulses will be inversely proportional to the speed of wheel 11. The output pulses of pulse generator 18 control multivibrator stage 28 supplying at its output the pulse sequence 128. The second output from stage 28, having a polarity suitable to the input to stage 31, for example negative, is applied to stage 31 and further to integrating stage 32. Integrator 32 converts the pulses to a slowly varying direct potential which is connected to control the length that stage 31 is unstable, that is which is connected to control the return of stage 31 to its stable state. The timing of stage 31 is so arranged that stage 31 will return to stable state just at the period of time when the first monostable multivibrator stage 28 is againtriggered into unstable condition. The pulses from circuit 31 are seen on timing diagram graph 131, FIG. 5.

Pulses 128, 131 are applied to coincidence stage 29. Coincidence stage 29 is so arranged that it provides a signal when neither input has any output applied thereto, that is when both signals 128, 131 areabsent; the output is seen at 129, FIG. 5.

Change in speed of wheel 11, which occurs upon braking, controls the stage31, over integrator 32, in such a manner that coincidence stage 29 does not become activated since the return to stable condition of the second monovibrator 31 will be followed immediately by another pulse from the first stage 28. Thus, no output will be obtained from stage 29 see the initial portions of graph 129, FIG. 5. If there is a change in the speed of wheel 11 beyond a predetermined limit, for example a change which will cause slipping of the wheel and skidding, the integrating stage 32 will not bring back stage 31 to stable condition in sufficient time so that another pulse from first multivibrator 128 will be available to block coincidence stage 29. The length of the pulse 131 thus no longer fills the gaps between a pair of consecutive pulses 128, and coincidence stage 29 will respond and cause a pulse, as seen at the righthand portion of graph 129. Amplifier 33, which may control electromechanical, or electrohydraulic apparatus, then can effect direct corrective action on braking cylinder system 15.

The circuits them selves should be so designed that small changes in the pulse shape or pulse width of the trailing edges of the pulse sequence 13] do not have an effect on coincidence stage 29 and cause it to become operative, so that minor variations in circuit components will have no influence on the operation of the circuit.

The system according to the present invention has the advantage that the pulse generator'operates without mechanically movable switches, so that the pulse source is free of any wear and tear, and reliable operation is ensured over the entire life of the equipment. The system of the present invention responds practically without any delay, and can act on the brake, or drive system immediately when wheel slippage might occur. Utilizing digital pulses in the control circuit has the additional advantagethat stray noise currents do not influence the operation. Acceleration measuring devices utilizing differentiating stages are subject to noise pulses and may give false readings upon the presence of superimposed AC components in the current supply lines, which are sometimes present in vehicle supply systems. The arrangement in accordance with the present invention further automatically takes into consideration that a higher braking (or accelerating) effort may be applied to the wheels before they will block, or slip through, respectively, if the vehicle carries a heavier load. Additionally, the arrangement in accordance with the present invention is independent of the surface condition of the way on which the wheel 11 runs, that is whether the road 12 is, for example dry, wet, or icy.

Reduced to essentials, the system of the present invention compares the individual elapsed time between a pulse and the immediately preceding pulse with the average elapsed time between a series of pulses. If this individual elapsed time period difiers from the average by an excessive amount (lack of overlap of pulses 128 and 131), circuit stage 29 responds.

FIG. 6 illustrates an optical arrangement to detect rotation, which may be used to replace transducer 18. A lamp 61 directs a beam of light 66 towards a reflecting surface 63 of a hexagonal reflecting element, such as a prism 62. Prism 62 reflects light beam 66, which is received in an entrance lens 64 and applied to a photoelectric responsive device, such as a photo diode 65, preferably including an inherent amplification function. Upon rotation of wheel 11, 6 pulses for each revolution of the wheel will be obtained from photosensitive device 65. Pulses from device 65 are applied to circuit 19 (FIG. 1) as schematically indicated by terminal 19".

Slipping of the wheel due to excessive accelerating forces, causing spinning or tum-through can be detected by a modification of the system, as illustrated in connection with FIGS. 7, 8 and 9, where elements similar to those previously described, but additional thereto have been given similar reference numerals, but with a prime mark. Elements previously discussed and described will not be referred to again.

Upon operation of an acceleration controller, such as a gas pedal 23', to cause acceleration of the vehicle, linkage 22 will open a controller 21', located in a fuel injection, or carburetor system for an internal combustion engine. As the throttle opens, motor 15 will provide increased torque which, transmitted over a clutch l6 and transmission 17 is applied to shaft 13 to drive the wheel. Wheel 11, as before, has the pulse transducer 18 arranged thereon (which may, if desired, take the form of the arrangement discussed in connection with FIG. 6) which provides output pulses to circuit 19. If the acceleration commanded by controller 23 is excessive, so that wheel 11 may spin, an output signal is obtained from the circuit 19, which is applied to the linkage to the fuel controller 21', or inherently to the fuel controller, to cause a lesser amount of fuel to be supplied to the engine, for example by closing of the throttle valve. Closing of the throttle valve, or decrease of the amount of fuel will lower the torque of motor and thus decrease the acceleration and avoid spinning.

The operation of the circuit in accordance with FIG. 8 is similar to that in accordance with FIG. 2. Additional to the circuit of FIG. 2, a NAND-circuit 29' is provided, which supplies an output signal if the first monostable multivibrator 28 supplies a pulse 128 (FIG. 9) while, simultaneously, a pulse 131 is obtained from a monostable multivibrator 31. To increase the reliability, the monostable multivibrator 31 is coupled to an additional integrating stage 32'. The length of the output pulses 131, as seen in FIG. 9, can thus be independent of the length of the output pulses 131 (FIG. 5). FIG. 9 illustrates the output pulses 129 of NAND-gate 29, which, applied over an amplifier 33 control the supply of fuel by device 21'.

The present invention has been described in connection with a wheel slip detection device for use in a vehicle operated by an internal combustion engine; the nature of the power supply, and the type of brakes used are independent of the present invention and, without departing from the scope of the inventive concept, suitable design modifications may be made to control any type of prime mover or brake system.

We claim:

1. Slip detection device to detect transition from rolling to slipping of a wheel (11) over a surface (12) upon acceleration or deceleration of the wheel comprising:

transducer means (18) coupled to the wheel and providing output pulses (118) having a repetition rate representative of wheel speed; a first monostable multivibrator 28); a second monostable multivibrator (31); the pulses (118) being connected to trigger said first monostable multivibrator 28) and to trigger said second monostable multivibrator (31);

means (32) connected to and controlling the unstable time of said second monostable multivibrator to be representative of elapsed time between pulses applied thereto;

means sensing change of elapsed time between pulses exceeding a predetermined amount of change, including a coincidence circuit (29) having the output of said first monostable multivibrator (28) applied to one input thereof and the output of said second monostable multivibrator (31) applied to a second input thereof;

and means (33) deriving an output signal from said sensing means.

2. Device according to claim 1, wherein the pulses applied to the input of said second multivibrator (31) are connected through said first multivibrator 28).

3. Device according to claim 1, wherein the means connected to and controlling the unstable time of the second monostable multivibrator (31) comprises an integrating network having the pulses from said first multivibrator (28) applied thereto and controlling the unstable period of said second multivibrator.

4. Device according to claim 1, in combination with a vehicle braking system, said means (33) deriving an output signal being connected to the vehicle braking system and supplying a control signal thereto upon detection of change of elapsed time between pulses in excess of a predetermined value.

5. Device according to claim 1, wherein said transducer means includes a magnetic transducer wheel mechanically coupled to said wheel (11), said transducer wheel having intermittently magnetic material located along its circumference;

and a yoke cooperating with said intermittent magnetic material, and a coil associated therewith, said coil having pulses induced therein upon rotation of said transducer wheel with respect to said yoke.

6. Device according to claim 5, wherein said transducer wheel comprises a plurality of magnets located at the circumference thereof, and of adjacent opposite polarity, and located in a magnetic circuit with said yoke.

7. Device according to claim 5, wherein said transducer wheel comprises a plurality of salient poles of ferromagnetic material and said coil is connected to a source of direct current.

8. Device according to claim 1, wherein said transducer means includes an optical transducer having a source of light and a light-sensitive element, and a movable reflector secured to rotate with said wheel (11) and reflecting light from said source to said photosensitive element, intermittently, upon rotation of said wheel.

9. Device according to claim 1, wherein said means connected to and controlling the unstable time of the second monostable multivibrator (31) includes an integrating circuit (32) having pulses with a repetition rate proportional to the repetition rate of said output pulses applied thereto and providing an electrical representation of average elapsed time between pulses;

and said coincidence circuit (29) is connected to compare the elapsed time between adjacent pulses with said electrical representation of averaged elapsed time.

10. Device according to claim 1, in combination with a vehicle driving system (15, 16', 17), said means (33) deriving an output signal being connected to the vehicle driving system and supplying a control signal thereto upon detection of increase of repetition rate of pulses in excess of a predetermined value.

11. Device according to claim 4, further in combination with a vehicle driving system and having a pair of second multivibrators (31, 31), a pair of integrating circuits (32, 32') forming a pair of means controlling a respective second multivibrator (31, 31) and each having pulses with a repetition rate proportional to the repetition rate of said output pulses applied thereto, each said integrating circuit providing an electrical representation of average elapsed time between pulses;

and said means sensing change of elapsed time between pulses including a pair of coincidence circuits (29, 29') each having the output of the first multivibrator (28) and a respective second multivibrator (31, 31') applied thereto and each comparing elapsed time between adjacent pulses with said electrical representation of average elapsed time, one coincidence circuit providing a first output signal when said comparison exceeds a certain value and the other coincidence circuit providing a second output signal when said comparison drops below a predetermined value. 

1. Slip detection device to detect transition from rolling to slipping of a wheel (11) over a surface (12) upon acceleration or deceleration of the wheel comprising: transducer means (18) coupled to the wheel and providing output pulses (118) having a repetition rate representative of wheel speed; a first monostable multivibrator (28); a second monostable multivibrator (31); the pulses (118) being connected to trigger said first monostable multivibrator (28) and to trigger said second monostable multivibrator (31); means (32) connected to and controlling the unstable time of said second monostable multivibrator to be representative of elapsed time between pulses applied thereto; means sensing change of elapsed time between pulses exceeding a predetermined amount of change, including a coincidence circuit (29) having the output of said first monostable multivibrator (28) applied to one input thereof and the output of said second monostable multivibrator (31) applied to a second input thereof; and means (33) deriving an output signal from said sensing means.
 2. Device according to claim 1, wherein the pulses applied to the input of said second multivibrator (31) are connected through said first multivibrator (28).
 3. Device according to claim 1, wherein the means connected to and controlling the unstable time of the second monostable multivibrator (31) comprises an integrating network having the pulses from said first multivibrator (28) applied thereto and controlling the unstable period of said second multivibrator.
 4. Device according to claim 1, in combination with a vehicle braking system, said means (33) deriving an output signal being connected to the vehicle braking system and supplying a control signal thereto upon detection of change of elapsed time between pulses in excess of a predetermined value.
 5. Device according to claim 1, wherein said transducer means includes a magnetic transducer wheel mechanically coupled to said wheel (11), said transducer wheel having intermittently magnetic material located along its circumference; and a yoke cooperating with said intermittent magnetic material, and a coil associated therewith, said coil having pulses induced therein upon rotation of said transducer wheel with respect to said yoke.
 6. Device according to claim 5, wherein said transducer wheel comprises a plurality of magnets located at the circumference thereof, and of adjacent opposite polarity, and located in a magnetic circuit with said yoke.
 7. Device according to claim 5, wherein said transducer wheel comprises a plurality of salient poles of ferromagnetic material and said coil is connected to a source of direct current.
 8. Device according to claim 1, wherein said transducer means includes an optical transducer having a source of light and a light-sensitive element, and a movable reflector secured to rotate with said wheel (11) and reflecting light from said source to said photosensitive element, intermittently, upon rotation of said wheel.
 9. Device according to claim 1, wherein said means connected to and controlling the unstable time of the second monostable multivibrator (31) includes an integrating circuit (32) having pulses with a repetition rate proportional to the repetition rate of said output pulses applied thereto and providing an electrical representation of average elapsed time between pulses; and said coincidence circuit (29) is connected to compare the elapsed time between adjacent pulses with said electrical representation of averaged elapsed time.
 10. Device according to claim 1, in combination with a vehicle driving system (15'', 16'', 17''), said means (33'') deriving an output signal being connected to the vehicle driving system and supplying a control signal thereto upon detection of increase of repetition rate of pulses in excess of a predetermined value.
 11. Device according to claim 4, further in combination with a vehicle driving system and Having a pair of second multivibrators (31, 31''), a pair of integrating circuits (32, 32'') forming a pair of means controlling a respective second multivibrator (31, 31'') and each having pulses with a repetition rate proportional to the repetition rate of said output pulses applied thereto, each said integrating circuit providing an electrical representation of average elapsed time between pulses; and said means sensing change of elapsed time between pulses including a pair of coincidence circuits (29, 29'') each having the output of the first multivibrator (28) and a respective second multivibrator (31, 31'') applied thereto and each comparing elapsed time between adjacent pulses with said electrical representation of average elapsed time, one coincidence circuit providing a first output signal when said comparison exceeds a certain value and the other coincidence circuit providing a second output signal when said comparison drops below a predetermined value. 